1. Field of the Invention
The present invention relates to engine cooling radiators and, more particularly, to radiator cores which utilize aluminum headers and plastic inlet/outlet tanks.
2. Description of Related Art
In the field of automobile engine-cooling radiators, the common method of construction of the radiator core (consisting of coolant-carrying tubes, cooling fins and inlet and outlet headers into which both ends of the tubes are sealed) is to form the core of brazed aluminum. Plastic inlet and outlet tanks are then connected to grooves in the headers, with a rubber gasket seal between them, and the mechanical connection of the headers to the tanks is by means of crimping or bending over header tabs over a lip or foot around the periphery of the plastic tanks. The assembly of a plastic tank to an aluminum header, with a rubber sealing gasket between them, constitutes a radiator or heat exchanger manifold. In service, the cooling system pressure in the tanks tends to force the tanks away from the headers and “unbend” the tabs, distorting the header grooves, and eventually allowing leakage past the gasket seal. Many design ideas have been tried, with varying success, to improve the integrity of the tank-to-header seal.
One such solution has been providing formed ribs on the header tabs, which strengthen the tabs against unbending. However, it has been shown that the biggest contributor to the failure of tank-to-header seals is not tab unbending, but rather header groove distortion. Therefore, strengthening the header tabs does not help much in preventing tank-to-header seal leakage.
Another potential solution has been the use of steel crimp strips to clamp the tanks to the headers, which has been used commercially, in spite of the increased cost associated with additional material and additional assembly labor. When properly applied, such crimp strips can help to keep the tanks clamped to the headers. However, in service, steel crimp strips suffer from serious corrosion problems resulting in unclamping and eventually severe leakage. Changing the material to stainless steel only increases the material cost and still leaves the problem of dissimilar materials between the crimp strips and the headers.
Another known approach to the tank-to-header leakage problem uses a header which has slots in the outer header groove wall. During assembly of the radiator, a rubber O-ring type gasket is placed in the header groove and a tank is assembled to the header, compressing the gasket. When the gasket is compressed the desired amount, a key strip is inserted through the slots in the header groove wall to retain the tank in place in the header groove at the desired amount of gasket compression. However, the seal gland formed by the bottom and sides of the header groove and the bottom of the tank foot is not a carefully-machined seal gland, which would permit carefully-controlled compression of the seal. Rather, the sheet metal header, with its header groove, bends and distorts under pressure, relieving gasket compression and allowing leakage.
It has been found that it is far better not to treat the header groove and tank foot as a typical seal gland with its demand for maintaining precise seal compression. Rather, the rubber seal should be trapped between the bottom of the tank foot and the walls and bottom of the header groove and compressed until it entirely fills the resulting volume as an incompressible fluid. Under such conditions, slight distortions of the header groove will not result in leakage. It then remains to minimize header groove distortion.
U.S. Pat. No. 7,640,971 to Kolb, entitled “Heat Exchanger Manifold Sealing System” addressed the overall tank-to-header leakage problem by increasing the depth of the header grooves and the length of the tank foot. In this design, the top of the foot of the plastic tank was provided with a small lip in order to concentrate the tab unbending force close to the bend of the tab. The result is that the unbending force tends not to unbend the tab, but rather to distort the header groove. Such header groove distortion leads to relieving gasket compression and allowing leakage over time.
Therefore, a need exists for a means for strengthening the header groove in order to resist deformation under service pressure, without significantly increasing material or labor costs.